Restructure the Kernel string table.

pkg/kernel/lib/binary/ast_to_binary.dart

Index: pkg/kernel/lib/binary/ast_to_binary.dart
diff --git a/pkg/kernel/lib/binary/ast_to_binary.dart b/pkg/kernel/lib/binary/ast_to_binary.dart
index 5092e69294be5f81bc22c0af49e849557176e5f6..cfc65fffe9b4a7063ccb11c6161f4bffa892750d 100644
--- a/pkg/kernel/lib/binary/ast_to_binary.dart
+++ b/pkg/kernel/lib/binary/ast_to_binary.dart
@@ -74,16 +74,17 @@ class BinaryPrinter extends Visitor {
     writeBytes(utf8Bytes);
   }
 
-  void writeStringTableEntry(String string) {
-    List<int> utf8Bytes = const Utf8Encoder().convert(string);
-    writeUInt30(utf8Bytes.length);
-    writeBytes(utf8Bytes);
-  }
-
   void writeStringTable(StringIndexer indexer) {
+    // Write the end offsets.
     writeUInt30(indexer.numberOfStrings);
+    int endOffset = 0;
+    for (var entry in indexer.entries) {
+      endOffset += entry.utf8Bytes.length;
+      writeUInt30(endOffset);
+    }
+    // Write the UTF-8 encoded strings.
     for (var entry in indexer.entries) {
-      writeStringTableEntry(entry.value);
+      writeBytes(entry.utf8Bytes);
     }
   }
 
@@ -1096,9 +1097,12 @@ class TypeParameterIndexer {
 
 class StringTableEntry implements Comparable<StringTableEntry> {
   final String value;
+  final List<int> utf8Bytes;
   int frequency = 0;
 
-  StringTableEntry(this.value);
+  StringTableEntry(String value)
+      : value = value,
+        utf8Bytes = const Utf8Encoder().convert(value);
 
   int compareTo(StringTableEntry other) => other.frequency - frequency;
 }